Method and apparatus for storage system

ABSTRACT

The present disclosure provides a method and an apparatus for a storage system. The storage system includes an active storage site and a standby storage site, and a logical unit number LUN for a storage pool of the active storage site is replicated to a LUN for a storage pool of the standby storage site to form a consistency group. The method comprises: creating a first LUN and a second LUN as mirrors of each other at the active storage site and the standby storage site, respectively; adding the mirrors formed by the first LUN and the second LUN to the consistency group; after the second LUN is added to the storage pool of the standby storage site, adding the first LUN to the storage pool of the active storage site.

RELATED APPLICATIONS

This application claim priority from Chinese Patent Application NumberCN201610150685.7, filed on Mar. 16, 2016 at the State IntellectualProperty Office, China, titled “METHOD AND APPARATUS FOR STORAGESYSTEM,” the contents of which is herein incorporated by reference inits entirety

FIELD

The present disclosure generally relates to storage technologies, andmore particularly, to a method and an apparatus for a storage system.

BACKGROUND

In a disaster recovery technical environment for a storage system, theremight exist multiple File level remote replication sessions, whichreplicate data from an active storage site to a standby storage site.While the data keeps growing, a storage pool such as the NASUser-defined pool protected by this remote replication session nearlyreaches its space limit. Therefore, when the storage pool of the activestorage site is close to its space limit, it is necessary to extend thespace of the storage pool and desire to keep the remote replicationsession functioning while extending the space of the storage pool.

In approaches in the prior art, it is necessary to first delete existingreplication session on the storage pool, then extend the storage pool onboth active and standby storage sites, and then re-create thereplication session. Since it may take days or even weeks for asynchronization process of a new replication session after its creation,after the previous replication session is deleted and before the newreplication session is synchronized, there is no protection on user datafor a rather long time period. If a disaster happens during this phase,there will be data loss.

SUMMARY

In view of the above technical problems existing in the prior art, oneof objectives of embodiments of the present disclosure is to provide amethod and an apparatus for a storage system, to solve at least one ofthe above technical problems existing in the prior art.

According to a first aspect of the present disclosure, there is provideda method for a storage system. The storage system includes an activestorage site and a standby storage site. A logical unit number (LUN) fora storage pool of the active storage site is replicated to a LUN for astorage pool of the standby storage site to form a consistency group.The method includes: creating a first LUN and a second LUN as mirrors ofeach other at the active storage site and the standby storage site,respectively; adding the mirrors formed by the first LUN and the secondLUN into the consistency group; after the second LUN is added into thestorage pool of the standby storage site, adding the first LUN into thestorage pool of the active storage site.

In some embodiments, the method may further include: in response to theactive storage site becoming unavailable, changing an originally activeLUN in the consistency group to be a standby LUN and changing anoriginally standby LUN to be an active LUN.

In some embodiments, the method may further include: before adding themirrors formed by the first LUN and the second LUN into the consistencygroup, determining that the first LUN and the second LUN aresynchronized.

In some embodiments, the method may further include: before adding thesecond LUN into the storage pool of the standby storage site,determining that the mirrors have been added into the consistency group.

In some embodiments, the method may further include: before adding thefirst LUN into the storage pool of the active storage site, determiningthat the second LUN has been added into the storage pool of the standbystorage site.

In some embodiments, the storage system may be a network-attachedstorage (NAS) system.

In some embodiments, the storage pools may include at least one of: avirtual NAS server, a file system, a snapshot, and a networkconfiguration.

According to a second aspect of the present disclosure, there isprovided an apparatus for a storage system. The storage system includesan active storage site and a standby storage site. A logical unit number(LUN) for the storage pool of the active storage site is replicated to aLUN for the storage pool of the standby storage site to form aconsistency group. The apparatus includes: a creating unit configured tocreate a first LUN and a second LUN as mirrors of each other at theactive storage site and the standby storage site, respectively; and anadding unit configured to add the mirrors formed by the first LUN andthe second LUN into the consistency group, the adding unit being furtherconfigured to, after the second LUN is added into the storage pool ofthe standby storage site, add the first LUN into the storage pool of theactive storage site.

According to a third aspect of the present disclosure, there is provideda computer-readable storage medium. The computer-readable storage mediumhas computer-readable program instructions stored thereon, and thesecomputer-readable program instructions are used for performing themethod according to the first aspect of the present disclosure.

According to a fourth aspect of the present disclosure, there isprovided a storage system. The storage system includes the apparatusaccording to the second aspect of the present disclosure.

As compared with the approaches in the prior art, the method andapparatus for the storage system according to the present disclosure mayat least achieve the following technical advantages. First, the existingreplication session may be kept functioning while extending the storagepool. Second, in any technical scenario of each phase of the procedureof extending the storage pool, data loss will not happen on the storagepool protected by the replication session.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the following detailed description with reference to theaccompanying drawings, the above and other objectives, features, andadvantages of example embodiments of the present disclosure will becomemore apparent. Several example embodiments of the present disclosurewill be illustrated by way of example but not limitation in the drawingsin which:

FIG. 1 schematically illustrates a diagram of a remote replicationsession for a storage system.

FIG. 2 schematically illustrates a flow chart of a method for a storagesystem according to an embodiment of the present disclosure.

FIG. 3A schematically illustrates a diagram of creating LUN mirrors atan active storage site and a standby storage site according to anembodiment of the present disclosure.

FIG. 3B schematically illustrates a diagram of adding the createdmirrors to a consistency group according to an embodiment of the presentdisclosure.

FIG. 3C schematically illustrates a diagram of extending a storage poolof the standby storage site according to an embodiment of the presentdisclosure.

FIG. 3D schematically illustrates a diagram of extending a storage poolof the active storage site according to an embodiment of the presentdisclosure.

FIG. 4 schematically illustrates a block diagram of an apparatus for astorage system according to an embodiment of the present disclosure.

FIG. 5 schematically illustrates a block diagram of a device that may beused to implement an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The principles and spirit of the present disclosure are described belowwith reference to several example embodiments shown in the figures. Itshould be appreciated that these embodiments are only intended to enablethose skilled in the art to better understand and implement the presentdisclosure, not to limit the scope of the present disclosure in anymanner.

FIG. 1 schematically illustrates a diagram of a remote replicationsession for a storage system 100. In FIG. 1, a file level remotereplication session is generally described by taking a network-attachedstorage NAS system as an example, but those skilled in the art myunderstand that the embodiments of the present disclosure may beequivalently applied to other storage systems.

As shown FIG. 1, the storage system 100 includes an active storage site110 and a standby storage site 120. The active storage site 110 and thestandby storage site 120 include storage pools 111 and 121,respectively. At the active storage site 110, a virtual NAS server(e.g., VDM) 112, together with all its file systems 113, snapshots 114and network configurations 115 etc., may be grouped into the storagetool 111. In the replication session from the active storage site 110 tothe standby storage site 120, data LUNs 116 for the storage pool 111 maybe replicated to data LUNs 122 for the storage pool 121 of the standbystorage site 120 by using a Consistency Group (CG) 130, wherein theconsistency group technique is a block level replication technique.

In the case that the active storage site 110 becomes unavailable due toa factor such as occurrence of a disaster, the storage system 100 mayread metadata stored in replica of the standby storage site 120, switchthe roles in the Consistency Group (CG) 130, re-create the NAS objects(VDM, file systems, etc.) on the data LUNs 122 of the standby storagesite 120, and seamlessly provide NAS service to the NAS clientsoriginally connected to the storage site 110. However, when the storagepool 111 on the active storage site 110 nearly reaches its space limit,it may be desirable to extend the storage pool 111 and possibly extendthe storage pool 121 of the standby storage site 120, while the remotereplication session is still working.

FIG. 2 schematically illustrates a flow chart 200 of a method for astorage system according to an embodiment of the present disclosure. Thestorage system to which the method 200 is directed includes an activestorage site and a standby storage site. A logical unit number LUN forthe storage pool of the active storage site is replicated to a LUN forthe storage pool of the standby storage site to form a consistencygroup. In some embodiments, the method 200 may be performed by anapparatus 400 for the storage system described later in combination withFIG. 4.

As shown in FIG. 2, the method 200 may enter step 201 after the start.In step 201, a first LUN and a second LUN as mirrors of each other arecreated at the active storage site and the standby storage site,respectively. The step 201 of the method 200 is described in more detailin conjunction with FIG. 3A.

FIG. 3A schematically illustrates a diagram of creating LUN mirrors atan active storage site and a standby storage site according to anembodiment of the present disclosure. As shown in FIG. 3A, an activestorage site 310 and a standby storage site 320 include storage pools311 and 321, respectively. In addition, the active storage site 310 mayfurther include a virtual NAS server (e.g., VDM) 312 and all its filesystems 113, snapshots 114 and network configurations 115 etc. Aconsistency group CG 330 is formed between the active storage site 310and the standby storage site 320.

In a technical scenario of a remote replication session for the storagesystem 300, in order to extend the space of the storage pool 311 of theactive storage site 310 and the space of the storage pool 321 of thestandby storage site 320, block storage LUN mirrors 340 and 350 may becreated in the storage system 300, and then the LUN mirrors 340 and 350wait for completing an initial replication. As shown in FIG. 3A, the LUNmirror 340 is formed by a LUN 341 at the active storage site 310 and aLUN 342 at the standby storage site 320, and the LUN mirror 350 isformed by a LUN 351 at the standby storage site 310 and a LUN 352 at thestandby storage site 320.

When the active storage site 310 becomes unavailable due to a factorsuch as occurrence of a disaster, the storage system 300 will switchroles in the consistency group CG 330, including roles in each pair ofmirror LUNs in the CG 330. The originally active storage site 310 willbecome standby, and the originally standby storage site 320 will becomeactive, and vice versa.

If a disaster happened in the active storage site 310 in the phase ofstep 201 of the method 200, there is no influence on the existingreplication session because LUN mirrors 340 and 350 have not yet beenadded into the consistency group CG 330. It should be appreciated thatFIG. 3A, for illustration purpose, shows only two LUN mirrors 340 and350 as an example, but in other embodiments, more or less LUN mirrorsare also possible.

Returning to FIG. 2, after step 201, the method 20X) may enter step 202.At step 202, mirrors formed by the first LUN and the second LUN areadded into the consistency group. The step 202 of the method 200 isdescribed in more detail in conjunction with FIG. 3B.

FIG. 3B schematically illustrates a diagram of adding the createdmirrors to a consistency group according to an embodiment of the presentdisclosure. As shown in FIG. 3B, the LUN mirrors 340 and 350 are addedto block storage consistency group CG 330. In other words, the LUN 341at the active storage site 310 and the LUN 342 at the standby storagesite 320, as well as the LUN 351 at the active storage site 310 and theLUN 352 at the standby storage site 320 are added into the consistencygroup CG 330.

After newly-created LUN mirrors 340 and 350 complete synchronization andare added into the consistency group CG 330, if the active storage site310 becomes unavailable due to a factor such as occurrence of adisaster, roles of the LUN mirrors 340 and 350 will be switched togetherwith other LUN mirrors in the consistency group CG 330.

In addition, the LUN mirrors 340 and 350 may be synchronized beforebeing added into the consistency group CG 330, otherwise the storagesystem 330 may reject the addition, to ensure the consistency group CG330 can be operated properly during disaster recovery.

Therefore, in some embodiments, the method 200 may further include:before adding the mirrors formed by the first LUN and the second LUNinto the consistency group, determining the first LUN and the second LUNare synchronized.

Returning to FIG. 2, after step 202, the method 200 may enter step 203.At step 203, after the second LUN is added into the storage pool of thestandby storage site, the first LUN is added into the storage pool ofthe active storage site. The step 203 of the method 200 is described inmore detail in conjunction with FIGS. 3C and 3D.

FIG. 3C schematically illustrates a diagram of extending a storage poolof the standby storage site according to an embodiment of the presentdisclosure. As shown in FIG. 3C, the storage pool 321 of the standbystorage site 320 may firstly be extended. That is, the LUNs 342 and 352in the LUN mirrors 340 and 350 are added into the storage pool 321 ofthe standby storage site 320.

It is noted that user data can write to the LUNs 342 and 352 only afterthe LUNs 342 and 352 are added into the storage pool 321. After the LUNs342 and 352 are added into the storage pool 321 of the standby storagesite 320, since there is no user's write operation at the standbystorage site 320, if there is a disaster happened in the active storagesite 310 after this phase, there will not be any data loss.

In addition, the storage system 300 may ensure that before extending thestorage pool 321 of the standby storage site 320, the LUNs 342 and 352are added into the consistency group CG 330 of the synchronizedreplication session. Hence, in some embodiments, the method 200 mayfurther include: before adding the second LUN into the storage pool ofthe standby storage site, determining that the mirrors have been addedinto the consistency group.

FIG. 3D schematically illustrates a diagram of extending a storage poolof the active storage site according to an embodiment of the presentdisclosure. As shown in FIG. 3D, after the extension of the storage pool321 of the standby storage site 320 is completed, the storage pool 311of the active storage site 310 may be extended. That is, the LUNs 341and 351 in the LUN mirrors 340 and 350 are added into the storage pool311 of the active storage site 310.

After the LUNs 341 and 351 are added into the storage pool 311 of theactive storage site 310, the user data can be written to the LUNs 341and 351. Furthermore, since the mirror LUNs 342 and 352 of the LUNs 341and 351 at the side of the standby storage system 320 are synchronizedwith the LUNs 341 and 351, if there is a disaster happened in the activestorage site 310 during this phase, there will not be any data loss.

In addition, the storage system 300 may check that the storage pool 321of the standby storage system 320 is firstly extended to ensure thatafter the storage pool 311 of the active storage system 310 is extended,if there is a disaster happened, there will not be potential data loss.Hence, in some embodiments, the method 200 may further include: beforeadding the first LUN into the storage pool of the active storage site,determining that the second LUN has been added into the storage pool ofthe standby storage site.

In some embodiments according to the present disclosure, the method 200may further include: in response to the active storage site 310 becomingunavailable, changing an originally active LUN in the consistency group330 to be a standby LUN and changing an originally standby LUN to be anactive LUN.

In some embodiments, the storage system 300 may be a network-attachedstorage NAS system. In some embodiments, the storage pools 311 and 321may include at least one of: a virtual NAS server, a file system, asnapshot, and a network configuration.

FIG. 4 schematically illustrates a block diagram of an apparatus 400 fora storage system according to an embodiment of the present disclosure.In the block diagram as shown in FIG. 4, dotted-line boxes are used torepresent optional units or components. Those skilled in the art mayunderstand that FIG. 4 only shows units or components in the apparatus400 closely related to the present disclosure. In specific practice, theapparatus 400 may include other functional units or components thatenable it to operate normally. In addition, units or components shown inFIG. 4 may be in necessary connection relations, but FIG. 4 does notdescribe these connection relations for the sake of brevity.

As described above, the storage system to which the apparatus 400 isdirected includes an active storage site and a standby storage site. Alogical unit number LUN for the storage pool of the active storage siteis replicated to a LUN for the storage pool of the standby storage siteto form a consistency group.

As shown in FIG. 4, the apparatus 400 includes a creating unit 401 andan adding unit 402. The creating unit 401 is configured to create afirst LUN and a second LUN as mirrors of each other at the activestorage site and the standby storage site, respectively. The adding unit402 is configured to add the mirrors formed by the first LUN and thesecond LUN into the consistency group. The adding unit 402 is furtherconfigured to, after the second LUN is added into the storage pool ofthe standby storage site, add the first LUN into the storage pool of theactive storage site.

In some embodiments, the apparatus 400 may further include: a switchingunit 403 configured to, in response to the active storage site becomingunavailable, change an originally active LUN in the consistency group tobe a standby LUN and change an originally standby LUN to be an activeLUN.

In some embodiments, the apparatus 400 may further include: a firstdetermining unit 404 configured to, before adding the mirrors formed bythe first LUN and the second LUN into the consistency group, determinethat the first LUN and the second LUN are synchronized.

In some embodiments, the apparatus 400 may further include: a seconddetermining unit 405 configured to, before adding the second LUN intothe storage pool of the standby storage site, determine that the mirrorshave been added into the consistency group.

In some embodiments, the apparatus 400 may further include: a thirddetermining unit 406 configured to, before adding the first LUN into thestorage pool of the active storage site, determine that the second LUNhas been added into the storage pool of the standby storage site.

In some embodiments, the storage system may be a network-attachedstorage NAS system. In some embodiments, the storage pools may includeat least one of: a virtual NAS server, a file system, a snapshot, and anetwork configuration.

FIG. 5 schematically illustrates a block diagram of a device 500 thatmay be used to implement an embodiment of the present disclosure. Asshown in FIG. 5, the device 500 includes a central processing unit (CPU)501 which is capable of performing various actions and processes inaccordance with computer program instructions stored in a read onlymemory (ROM) 502 or computer program instructions loaded from a storageunit 508 to a random access memory (RAM) 503. In the RAM 503, variousprograms and data needed by operation of the device 500 might be stored.The CPU 501, the ROM 502 and the RAM 503 are connected to one anothervia a bus 504. An input/output (I/O) interface 505 is also connected tothe bus 504.

Multiple components in the device 500 are connected to the I/O interface505: an input unit 506 including a keyboard, a mouse or the like; anoutput unit 507 such as various displays, loudspeaker or the like; thestorage unit 508 such as a magnetic disk, optical disk or the like, anda communication unit 509 such as a network card, a modem, a wirelesscommunication transceiver, or the like. The communication unit 509permits the device 500 to exchange information/data with other devicesthrough for example a computer network such as the Internet and/orvarious communication networks.

The processes and processing described above, for example, method 200,may be implemented by a processing unit 501. For example, in someembodiments, the method 200 may be implemented as a computer softwareprogram which is tangibly included in a machine-readable medium, forexample the storage unit 508. In some embodiments, a part or entirety ofthe computer program may be loaded and/mounted on the device 500 via theROM 502 and/or communication unit 509. When the computer program isloaded to the RAM 503 and implemented by the CPU 501, it may execute oneor more steps of the method 200 described above.

In the description of the embodiments of the present disclosure, theterm “comprise” and like wording should be understood to be open-ended,i.e., to mean “including but not limited to.” The term “based on” shouldbe understood as “at least partially based on.” The term “an embodiment”or “the embodiment” should be understood as “at least one embodiment.”

It should be appreciated that embodiments of the present disclosure maybe implemented by hardware, software or a combination of the softwareand combination. The hardware part may be implemented using a dedicatedlogic; the software part may be stored in the memory, executed by anappropriate instruction executing system, e.g., a microprocessor or adedicatedly designed hardware. Those ordinary skilled in art mayunderstand that the above apparatus and method may be implemented usinga computer-executable instruction and/or included in processor controlcode. In implementation, such code is provided on a medium such as aprogrammable memory, or a data carrier such as optical or electronicsignal carrier.

In addition, although operations of the present methods are described ina particular order in the drawings, it does not require or imply thatthese operations must be performed according to this particularsequence, or a desired outcome can only be achieved by performing allshown operations. On the contrary, the execution order for the steps asdepicted in the flowcharts may be varied. Additionally or alternatively,some steps may be omitted, a plurality of steps may be merged into onestep, or a step may be divided into a plurality of steps for execution.It should be appreciated that features and functions of two or moredevices according to the present disclosure may be embodied in onedevice. On the contrary, features and functions of one device asdepicted above may be further divided into and embodied by a pluralityof devices.

Although the present disclosure has been depicted with reference to aplurality of embodiments, it should be understood that the presentdisclosure is not limited to the disclosed embodiments. The presentdisclosure intends to cover various modifications and equivalentarrangements included in the spirit and scope of the appended claims.

We claim:
 1. A method for a storage system, the storage system includingan active storage site and a standby storage site, a logical unit number(LUN) for a storage pool of the active storage site being replicated,during a functioning remote replication session, to a LUN for a storagepool of the standby storage site, at least the LUN for the storage poolof the active storage site and the LUN for the storage pool of thestandby storage site forming a consistency group, the method comprising:creating, using one or more processors and memory, a mirror relationshipbetween a first LUN at the active storage site and a second LUN at thestandby storage site; adding the first LUN and the second LUN in themirror relationship into the consistency group; and having added thefirst LUN and the second LUN in the mirror relationship into theconsistency group, extending the storage pool of the active storage sitewhile keeping the remote replication session functioning, the extendingof the storage pool of the active storage site including (i) adding thesecond LUN into the storage pool of the standby storage site, and (ii)having added the second LUN into the storage pool of the standby storagesite, adding the first LUN into the storage pool of the active storagesite.
 2. The method according to claim 1, further comprising: inresponse to the active storage site becoming unavailable, changing anoriginally active LUN in the consistency group to be a standby LUN andchanging an originally standby LUN to be an active LUN.
 3. The methodaccording to claim 1, further comprising: before adding the first LUNand the second LUN in the mirror relationship into the consistencygroup, determining that the first LUN and the second LUN aresynchronized.
 4. The method according to claim 1, further comprising:before adding the second LUN into the storage pool of the standbystorage site, determining that the first LUN and the second LUN in themirror relationship have been added into the consistency group.
 5. Themethod according to claim 1, further comprising: before adding the firstLUN into the storage pool of the active storage site, determining thatthe second LUN has been added into the storage pool of the standbystorage site.
 6. The method according to claim 1, wherein the storagesystem is a network-attached storage (NAS) system.
 7. The methodaccording to claim 6, wherein each of the storage pool of the activestorage site and the storage pool of the standby storage site includesat least one of: a virtual NAS server, a file system, a snapshot, and anetwork configuration.
 8. A system, comprising: a storage systemincluding an active storage site and a standby storage site; a logicalunit number (LUN) for a storage pool of the active storage site beingreplicated, during a functioning remote replication session, to a LUNfor a storage pool of the standby storage site, at least the LUN for thestorage pool of the active storage site and the LUN for the storage poolof the standby storage site forming a consistency group; andcomputer-executable program logic encoded in memory of one or morecomputers using the storage system, wherein the computer-executableprogram logic is configured for the execution of: creating, using one ormore processors and memory, a mirror relationship between a first LUN atthe active storage site and a second LUN at the standby storage site;adding the first LUN and the second LUN in the mirror relationship intothe consistency group; and having added the first LUN and the second LUNin the mirror relationship into the consistency group, extending thestorage pool of the active storage site while keeping the remotereplication session functioning, the extending of the storage pool ofthe active storage site including (i) adding the second LUN into thestorage pool of the standby storage site, and (ii) having added thesecond LUN into the storage pool of the standby storage site, adding thefirst LUN into the storage pool of the active storage site.
 9. Thesystem of claim 8, wherein the computer-executable program logic isfurther configured for the execution of: in response to the activestorage site becoming unavailable, changing an originally active LUN inthe consistency group to be a standby LUN and changing an originallystandby LUN to be an active LUN.
 10. The system of claim 8, wherein thecomputer-executable program logic is further configured for theexecution of: before adding the first LUN and the second LUN in themirror relationship into the consistency group, determining that thefirst LUN and the second LUN are synchronized.
 11. The system of claim8, wherein the computer-executable program logic is further configuredfor the execution of: before adding the second LUN into the storage poolof the standby storage site, determining that the first LUN and thesecond LUN in the mirror relationship have been added into theconsistency group.
 12. The system of claim 8, wherein thecomputer-executable program logic is further configured for theexecution of: before adding the first LUN into the storage pool of theactive storage site, determining that the second LUN has been added intothe storage pool of the standby storage site.
 13. The system of claim 8,wherein the storage system is a network-attached storage (NAS) system.14. The system of claim 13, wherein each of the storage pool of theactive storage site and the storage pool of the standby storage siteincludes at least one of: a virtual NAS server, a file system, asnapshot, and a network configuration.
 15. A computer program productfor a storage system, the storage system including an active storagesite and a standby storage site, a logical unit number (LUN) for astorage pool of the active storage site being replicated, during afunctioning remote replication session, to a LUN for a storage pool ofthe standby storage site, at least the LUN for the storage pool of theactive storage site and the LUN for the storage pool of the standbystorage site forming a consistency group, the computer program productcomprising: a non-transitory computer readable medium encoded withcomputer-executable code, the code configured to enable the executionof: creating, using one or more processors and memory, a mirrorrelationship between a first LUN at the active storage site and a secondLUN at the standby storage site; adding the first LUN and the second LUNin the mirror relationship into the consistency group; and having addedthe first LUN and the second LUN in the mirror relationship into theconsistency group, extending the storage pool of the active storage sitewhile keeping the remote replication session functioning, the extendingof the storage pool of the active storage site including (i) adding thesecond LUN into the storage pool of the standby storage site, and (ii)having added the second LUN into the storage pool of the standby storagesite, adding the first LUN into the storage pool of the active storagesite.
 16. The computer program product of claim 15, wherein the code isfurther configured to enable the execution of: in response to the activestorage site becoming unavailable, changing an originally active LUN inthe consistency group to be a standby LUN and changing an originallystandby LUN to be an active LUN.
 17. The computer program product ofclaim 15, wherein the code is further configured to enable the executionof: before adding the first LUN and the second LUN in the mirrorrelationship into the consistency group, determining that the first LUNand the second LUN are synchronized.
 18. The computer program product ofclaim 15, wherein the code is further configured to enable the executionof: before adding the second LUN into the storage pool of the standbystorage site, determining that the first LUN and the second LUN in themirror relationship have been added into the consistency group.
 19. Thecomputer program product of claim 15, wherein the code is furtherconfigured to enable the execution of: before adding the first LUN intothe storage pool of the active storage site, determining that the secondLUN has been added into the storage pool of the standby storage site.20. The computer program product of claim 15, wherein the storage systemis a network-attached storage (NAS) system.